My friend, Brian, concerned for my sanity, did some searching and sent me this:
From: Brian Yoder <XXXXXXXXXXXXXXXXXXXXXXX>
To: Sean Conner <sean@conman.org>
Subject: El Capitan: Rootless "feature"
Date: Thu, 15 Oct 2015 14:23:33 -0400
> From: http://apple.stackexchange.com/questions/193368/what-is-the-rootless-feature-in-el-capitan-really [1]
> > When you upgrade to El Capitan, it moves any "unauthorized" files from restricted areas to /Library/SystemMigration/History/Migration-(someUUID)/QuarantineRoot/.
>
Really?
>
```
[spc]marvin:~>ll /Library/SystemMigration/History/Migration-0C65E56F-4185-42B0-BBE8-5537E4FDEE38/QuarantineRoot/usr/bin/
total 92472
-rwxr-xr-x 1 root wheel 60212 Dec 6 2005 bbdiff
-rwsr-xr-x 1 root wheel 86416 Dec 6 2005 bbedit
-rwxr-xr-x@ 1 root wheel 21226488 Feb 4 2005 emacs (from old Mac)
-rwxr-xr-x@ 1 root wheel 21226488 Feb 4 2005 emacs-21.2.1
-rwxr-xr-x 1 root wheel 1511312 Dec 21 2010 pkgbuild
-rwxr-xr-x 1 root wheel 1605200 Dec 21 2010 productbuild
-rwxr-xr-x 1 root wheel 1440848 Dec 21 2010 productsign
-rwxr-xr-x 1 wlofie staff 1195132 May 14 2010 synergyc
-rwxr-xr-x 1 wlofie staff 1751764 May 14 2010 synergys
-rwxr-xr-x 1 root wheel 3561 Jul 12 2007 zegrep (from old Mac)
-rwxr-xr-x 1 root wheel 3561 Jul 12 2007 zfgrep (from old Mac)
-rwxr-xr-x 1 root wheel 103 Jul 12 2007 zless (from old Mac)
[spc]marvin:~>
```
Oh.
There are my missing executables [2]! In /usr/bin! And … owned by wlofie [3]? How did—
Nevermind!
I found them!
I had to copy them out of that directory to $HOME/bin so they won't get blown away again. Then I had to tweak “System Preferences → Security & Privacy → Privacy” to allow Terminal and “sshd-keygen-wrapper” to have control over my computer, then I can run synergys in the foreground, and it works! If I let synergys run in the background (as it does by default) then El Presidente de Por Vida [4] prevents it from doing anything useful.
But I got it to work!
So now I'm back to where I was on October 1^st [5]!
Woot!
[3] https://www.google.com/search?q=wlofie+site%3Aboston.conman.org